The pump can be hydraulically coupled to a low-pressure fuel supply device by means of the valve. The output end of said pump is hydraulically coupled to the nozzle unit. The start of injection and the injection quantity are determined by the valve and its valve drive. The compact construction of the pump-nozzle apparatus results in a very low high-pressure volume and a high degree of hydraulic rigidity. Therefore, very high injection pressures of approximately 2000 bar are possible. This high injection pressure, in conjunction with the ability to control the start of injection and the injection quantity in an effective manner, permit a considerable reduction in emissions and at the same time low fuel consumption when using the internal combustion engines.
DE 198 35 494 C2 discloses a pump-nozzle apparatus having a pump and a valve with a valve element which controls the hydraulic coupling of a discharge space to an outlet channel. The outlet channel is hydraulically coupled to the pump and a nozzle unit. An inlet channel is provided which is hydraulically coupled to the discharge space. The valve element has an associated piezoelectric valve drive which can be used to move the valve element between two end positions. When the valve element is in a first end position, the outlet channel is hydraulically coupled to a discharge space and this, in turn, is hydraulically coupled to the inlet channel. When the valve element is in a second end position, the outlet channel is hydraulically decoupled from the discharge space and the valve element is arranged in a valve seat of the valve.
When the valve element is in the first end position, fluid is drawn from the inlet channel by the pump via the discharge space and outlet channel during a delivery stroke of the pump. During a working stroke of a piston of the pump, fluid is forced back from the pump to the inlet channel via the outlet channel and the discharge space when the valve element is in the first end position. When the valve element is in the second end position, no fluid can be forced back and the pump piston generates high pressure since the outlet channel is not hydraulically coupled to the discharge space and the inlet channel during the delivery stroke of the pump piston. When a prescribed pressure threshold is exceeded, a nozzle needle of the nozzle unit opens a nozzle of the nozzle unit and fluid is injected. The end of injection is determined by the valve element being moved to its first end position by means of the actuating drive and fluid thus flowing back to the discharge space and the inlet channel via the outlet channel, this resulting in the pressure in the pump and therefore also in the nozzle unit decreasing, which in turn leads to the nozzle unit being closed.
Low pollutant emissions from an internal combustion engine in which the pump-nozzle arrangement is arranged and precise control of the internal combustion engine mean the pump-nozzle apparatus has to meter fuel in a precise manner. This in turn means that the piezo-controlled valve of the pump-nozzle apparatus has to be driven in a manner which can be reproduced and is stable over the long term.
WO 03/081007 A1 discloses a method and an apparatus for detecting the impact time of a valve needle of a piezoelectric control valve. The piezoelectric control valve is used in a pump-nozzle unit for injecting fuel into an internal combustion engine. The impact time of the valve needle of the piezoelectric control valve of the pump-nozzle unit is determined by evaluating the piezoelectric voltage and/or the piezoelectric current.
Furthermore, WO 03/104633 A1 discloses a method and an apparatus for measuring and controlling the closing and opening times of a piezoelectric control valve, in which the period of time required for a valve needle of a control valve of a piezoelectric pump-nozzle unit to move from a first end position to a second end position is measured, with the response time of the control valve being taken into account. In this case, the period of time is determined as a function of the voltage applied to the control valve and/or of the current applied. An actuating signal which is used to move the control valve from the first end position to the second end position is also generated, with the actuating signal being generated at a time during which it is ensured that the pressure in the control valve and in the injection nozzle during the measurement process corresponds largely to the pressure in the low-pressure fuel region.
In addition, DE 196 52 801 C1 discloses a method and an apparatus for driving at least one capacitive actuating element, said capacitive actuating element being used, in particular, in a piezoelectrically operated fuel-injection valve of an internal combustion engine. The power of the actuator and/or the charge quantity of the capacitive actuating element, which is applied to the actuator for operating purposes, are/is regulated when the capacitive actuating element is being driven. The respective prespecified setpoint values are selected as a function of various operating parameters of the internal combustion engine.